Method of insulating and covering electrical conductors



Patented Feb. 23, 1943 METHOD OF INSULATING AND COVERING ELECTRICAL CONDUCTORS Edward D. Youmans, Montclair, and William F. Lamela, East Paterson, N. J., assignors to The Okonite Company, Passaic, N. J., a corporation of New Jersey No Drawing. Application September 13, 1939, Serial No. 294,666

1 Claim.

Our invention relates to an improved method of covering wire, more particularly to the covering of a wire with an insulating compound and an outer protective composition covering.

More specifically our invention is directed to an improved method for the application of an outer covering to the rubber compound insulation of an electrical conductor in replacement of the conventional saturated fibrous braid.

Still more specifically our invention has for an object the provision of a method involving application of the rubber compound insulation direct to the conductor by a strip method as distinguished from extrusion, and the application also by the strip method, directly about this insulation, of a covering possessing superior characteristics as compared with the conventional saturated fibrous braid used heretofore.

Before proceeding with a detailed description of our invention, it may be well for clarity of description to make reference to covered, rubbercompound-insulated conductors as conventionally constructed prior to our invention.

These prior constructions embody a rubber compound insulation and a covering of saturated fibrous braid. The function of the fibrous braid is primarily to protect the' insulation against mechanical injury and sun-checking. However, these braids soon deteriorate and rot away from the insulation due to the destructive influence of molds and bacteria, especially in the presence of moisture. Then again, the surface resistivity of these braids is low, with the result that the braids frequently develop static or corona discharge in service in ducts at from 2000 to 5000 volts. Cotton braids also have other disadvantages, such as their infiammability, lack of flexibility at low temperatures and poor resistance to abrasion, acids, alkalis, oils and other chemicals.

We intend employing a composition outer covering, comprising polymerized chlorinated butadiene or plastic polymer, instead of the saturated fibrous braids heretofore used. This outer covering or sheath has excellent mechanical properties and resistance to abrasion, acids, alkalis, oil, etc., and is immune to mold growth. It protects the insulation against sun-checking, is flexible at low temperatures. resistant to heat, and inasmuch as it contains chemically combined chlorine it is relatively non-inflammable. Furthermore, this composition does not develop static or corona discharge when in service in ducts at from 2000 to 5000 volts, and since it has excellent ozone resistance it will not readily be attacked or corona cut in the event some ozone is formed.

In the practice of our invention an insulating compound, which is to be applied directly to the conductor to be insulated, is put through a feeding mill for calendaring. When the proper thickness has been attained the compound is cut into strips and wound upon a suitable cylinder or roll with cloth interposed between adjacent layers. Eventually this material is rewound, the cloth being removed in the process, and the strip spliced together to form a length say of 3000 feet.

When a conductor is to be insulated, the con-.

ductor and the continuous insulating strip are led through suitable apparatus which shapes the insulation about the conductor. This operation is repeatedas many times as necessary to build up an insulating layer of the desired thickness.

The outer covering, especially on small cables, has to be applied about the insulation in a thin layer only, say for example a covering fifteen mils thick, and for this reason it is not practicable to apply it by the extrusion method.

Accordingly we proceed as follows: The composition which is to constitute the outer covering comprises polymerized chlorinated butadiene or plastic polymer. This material is first milled, and then calendered upon a tin sheet which is first given a thin coating of shellac or any other mould solution. The thickness of the tin sheet depends on the size of cable to be insulated and ranges from twelve to thirty mils and the layer of composition applied to it may be as thin as ten mils. The thin layer of mould solution which is applied to the tin cause the uncured composition to adhere to the tin backing and permits free stripping of the tin after vulcanization has been completed.

After the outer covering composition has been applied to the tin sheet, the assembly is cut into strips of the necessary width, th ends of the strips joined and then the continuous strip thus produced together with the insulated conductor are run through the same or a similar machine as was employed for application of the main wall of insulating compound, which, as will be appreciated, shapes the tin-backed composition about the conductor insulation. As the tinbacked composition moves to this apparatus it passes along a steam heated table or other suitable equipment which slightly warms the composition. This serves to promote adherence of the composition to the insulating compound and a smooth;;.' dense,: polished; surface on the sheath;

We :have foundthat'byfapplyingboth'itheinsu lation-x? andqLthe outer covering-hot j acket by the strip methodjasqhereinabove" described; very ac curate control "is-assured. overirthevth'i'ckness of the; insulation andv jacket tion and the outer covering without'recourse"to Chloro-2-butadiene-1-3 plastic polymer 50-60 Magnesium oxide; 2-6 Wood rosin -3 5 Factice 9-4" Carbon -10 Inert mineral ingredients 20-0 Softening oils" 0-5" Softeners 0-6 10 Sulphur 0-1 Accelerator 0-21 ,Zinc' OXidei;.L s 2-6 This is .015 0,material advantage as wilLbe appreciatedzbythose-skilled in thisarta Wefin'd' also thatywe'obtainja firm Per cent,

utes. In compounding, the ingredients are added to the polymer in the order-given.

adhesives or cements; Furthermore, 'the. insuia-, tion-zand outer covering :can' be run inf'th'e same cute: 5 covering-1; eomposittonticauses' the uncured composition to :adhere' to-th'e. tina 'during the" calenderingoperationzrand {permits ,free stripping oi" the, tin setter-1 vulcanization-, leaving. a: dense,

smooth;shi'ghlyypolishedvmace. a

The.,.;resu1tingw:ja'cket I on "sheath compound in i addition to'rserving as: i a mechanical "protector has: good electrical" characteristics rwhich 'pro-' even after-prolonged immersionxin water. brous braids of course provide little, if any, insulatio and; upon immersion bec icon; ductix'm; 1

We have obtaimedsa tisfactor y; results with (the,

following-compound; which, itbe undferstoodg. is set up "merely; as: an. example? of a suitable material for the 'o utertcovering' or jacket, it being understood that the formula maybe varied with- What w egclaimeis: The continuousmethod of insulating electrical conductors and bonding an outerprotective layer I 120 thereto, which method comprises continuously" applying one or more layers otanunvulcan-ized rubber insulating compound to the conductor by" the'strip method until an insulating layer-*0!" the, desired thickness has beenbuilt up,'con-' a tinuously, advancing, an elongated: composite strip, composed of tincoatedronone face withv ahmould' solution and a superimposed layer of uncured compound composed mainly of polymer- I ized chlorinated butadiene calendered thereto,

p so A 7 vides' additional"insu'lationu:over"the conductor; bring the'stnp and the Vulcanized sition passing through aheated zone 'soas,toheat the butadiene and promote-its adherence to theinsulating compound, shaping, thenelongatedstrip transversely of its length about the uncured insulating compound; curing the insuo lating compound and butadiene, and finally reoutz,de'parting fromthe", spirit: and scope oi f our i invention:

moving thetin. I I EDWARD DJYOUMANSL- Thisstockl has iacuring range of 250 F. for: r-onehundred minutes to 305 F. for sixt minbond 7 and: strong .adhesion zhetween ethe .-insula-s 15 y 

